Ultrasound diagnosis apparatuses may be used for diagnosing stenoses in blood vessels. For example, an ultrasound diagnosis apparatus obtains blood flow information by using a color Doppler mode or a pulse Doppler mode. Blood flow rates, which serve as a type of blood flow information, become faster and slower repeatedly at regular intervals. For example, medical doctors and the like make a diagnosis as to whether a stenosis has occurred in a blood vessel or not by comparing the ratio between the largest value and the smallest value among obtained blood flow rate values with a reference value.
Further, to improve the precision level of the diagnosis, it is necessary to obtain accurate blood flow information. To obtain accurate blood flow information, for example, it is desirable to arrange the angle (expressed as θ degrees) formed by the transmission direction of an ultrasound beam transmitted from an ultrasound probe and the direction in which the blood vessel extends (hereinafter, “blood vessel extending direction”) so as to be an angle desired by the operator.